In the prior art, there are navigation devices, portable telephones and similar which provide navigation of routes for vehicles and persons using position information from the GPS (Global Positioning System).
For example, Japanese Patent Laid-open No. 8-334337 discloses a current position calculation device capable of returning to an initial value a travel distance coefficient, used to calculating travel distances, which is corrected in accordance with vehicle travel.
In this current position calculation device, an MPU multiplies the number of output pulses from a vehicle velocity sensor, counted by a counter, by a travel distance coefficient to calculate the travel distance of the vehicle, and estimates the traveled road being traveled by the vehicle and the current position of the vehicle on the traveled road based on map data stored on a CD-ROM, the vehicle direction of advance determined from measured values of an angular velocity sensor and bearing sensor, and the distance traveled by the vehicle. Here, the travel distance coefficient is dynamically corrected according to the difference between the direction of the traveled road at the estimated current position and the direction of advance of the vehicle. When the MPU is instructed by a switch to correct the estimated current position, the travel distance coefficient is returned to an initial value in response to the instruction.
Thus by returning to an initial value as necessary a travel distance coefficient which is used to calculate travel distances, and which is correct as the vehicle travels, the current position of the vehicle can be accurately detected.
There is a radial error of approximately 10 meters in the position information from the GPS; by means of a current position calculation device such as that described in Japanese Patent Laid-open No. 8-334337 and ordinary vehicle navigation systems, position information when there is motion equal to or greater than a prescribed distance exceeding this error is used to detect the current position.